Electronic devices have been steadily miniaturized. In order to cope with miniaturization of electronic devices, BGA system package substrates (hereinafter referred to as a “BGA package substrate”) having an electrode geometry in which solder balls for electrically connecting a semiconductor chip to a substrate are arranged vertically and horizontally have been used in recent years.
Along with an increase in the amount of information inputted and outputted to and from a semiconductor chip, the number of solder balls provided in a BGA package substrate is continuously increasing. In addition, along with an increase in the amount of information processed by a semiconductor chip, the power consumption of the semiconductor chip is increasing. Thus, the solder balls provided in a BGA package substrate are demanded to have a size which does not cause the current density to exceed an allowable current density. That is, a large number of solder balls are provided in a BGA package substrate, each of the solder balls having a size which does not cause the current density to exceed an allowable current density. Thus, the pitch between solder balls provided vertically and horizontally in a BGA package substrate is inevitably reducing.
Meanwhile, when solder balls provided in a BGA package substrate are brought into contact with each other, a short circuit occurs. Thus, the solder balls provided in a BGA package substrate are demanded to be fused to the BGA package substrate in a state where the solder balls are spaced apart. However, when a solder ball is fused to a BGA package substrate, flux applied to the solder ball spreads over a land, and thus the solder ball may be moved through following the flow of the flux spreading over the land. When adjacent solder balls are moved in respective directions which allow the solder balls to approach each other, a short circuit may occur due to contact between the solder balls. When the pitch between lands is reduced, a short circuit due to contact between solder balls is likely to occur.
The followings are reference documents.
[Document 1] Japanese Laid-open Patent Publication No. 11-87427 and
[Document 2] Japanese Laid-open Patent Publication Nos. 10-256418.